Inhibitory effects of pre- and posttest drugs on mouse-killing by rats.

Mouse-killing in rats was gradually inhibited by repeated posttest injections of d-amphetamine (1.5 mg/kg), l-amphetamine (1.5 mg/kg) or pilocarpine (7.5 mg/kg), but not by control substances. Of these drugs, only d-amphetamine inhibited killing when given prior to a mouse-killing test. Further experiments suggested that anorexia per se did not contribute to drug-induced inhibitory effects, but that changes in internal state were important to the development of inhibition. Pretest injections appear to inhibit predatory killing by a direct pharmacological action on some target site or sites, while posttest injections produce a learned aversion to predatory killing.